1. Field of the Invention
The field of the invention relates to a circuit and method for predicting where timing errors may occur.
2. Description of the Prior Art
With the progressive scaling down of semiconductor, such as CMOS, device sizes, these devices are now nearing their physical and reliability limits. This has resulted in designs that were manufactured correctly wearing out and becoming unreliable over time due to mechanisms such as negative bias temperature instability (or NBT1) and gate oxide breakdown.
The aging effects on these devices can cause a design that functions correctly initially to develop timing errors over time.
This problem has been addressed in some designs by increasing margins in the design based on the worst degradation that it is predicted devices might suffer during the lifetime of the device. However, this approach leads to a decrease in the performance of the design and therefore is not appropriate for high performance devices.
This problem has been addressed in a Razor design described by Ernst et al. in “Razor a low-power pipeline based on circuit-level timing speculation” by sampling the data with a delayed clock and where errors are detected implementing a recovery phase to correct them. A drawback of this approach is that it only detects errors after they have taken place and it then requires a recovery phase and thus, there are significant performance overheads once an error has occurred.
A further way of addressing the problem is described in Agarwal et al. in “Circuit failure prediction and its application to transistor aging”. In this technique a flip-flop design is used which can predict the timing errors before they happen. An inverted delayed clock is used to sample the data and generate an error signal if a transition is detected in a window before the transition happens. A drawback in this technique is the significant cost in area in implementing the delayed clock and stability checker.
It would be desirable to be able to detect timing errors in a system before they happen without unduly increasing the area of the design.